Background

Milia are benign, keratinous cysts that commonly manifest as tiny white bumps on the face of the newborn (see the image below). When present on the gum margin and midline palate they are referred to as Bohn nodules and Epstein pearls, respectively. Milia can be broadly categorized into primary and secondary types. Congenital milia in newborns account for the vast majority of primary milia. Primary milia may also occur in association with one of several genodermatoses or sporadically without associated findings. Secondary milia may be associated with an underlying skin disease, medications, or trauma.

In 2008, Berk and Bayliss published an updated classification of milia, as follows
[1] :

Primary milia is as follows:

Congenital

Benign primary milia of children and adults

Milia en plaque

Nodular grouped milia

Multiple eruptive milia

Nevus depigmentosus with milia

Genodermatosis-associated

Secondary milia is as follows:

Disease-associated

Medication-associated

Trauma-associated

Congenital milia occur in nearly half of healthy newborns and are typically present at birth, although their onset may be delayed in premature neonates.
[2] Lesions typically spontaneously resolve within weeks. Congenital milia predominate on the face, and the nose is frequently affected.

Benign acquired milia of children and adults also occur spontaneously; however, like other acquired milia, they have a tendency to persist without treatment. Benign acquired milia of children and adults favor the eyelids, cheeks, forehead and genitalia.

Multiple eruptive milia describes acquired and widespread milia that appear rather abruptly over weeks to months. Multiple eruptive milia may be associated with a genodermatosis or inherited in an autosomal dominant fashion without other apparent anomalies; however, in most cases they occur sporadically.
[3]

In children, traumatic milia most commonly manifest following abrasions or burns. Milia have also been reported following skin grafting.
[8] Milia may occur in association with blistering skin diseases. Epidermolysis bullosa and porphyria cutanea tarda are the classic examples. Milia associated with topical corticosteroid use is rarely reported.
[9]

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Pathophysiology

Histopathologic studies support the notion that primary milia arise from the lower infundibular sebaceous collar of the vellus hair, whereas secondary milia are more commonly derived from eccrine ducts.
[10, 11]

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Epidemiology

Frequency

Congenital milia are common, affecting 40-50% of healthy newborns. Infants born prematurely are less commonly affected although their onset may be delayed.

Race

No racial predilection is observed.

Sex

In general, milia occur equally in males and females. Milia en plaque is more common in females.

Age

Milia can affect persons of any age, but are most commonly seen in the neonatal period. Onset can be delayed for days to weeks in neonates born prematurely. Milia en plaque is most common in middle-aged adult females.

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Prognosis

Congenital milia are benign cysts with a tendency for spontaneous resolution without scarring.

Acquired milia may persist without treatment.

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Patient Education

Educate the family about the benign course of milia and tendency towards spontaneous resolution without scarring.

Robert A Schwartz, MD, MPH Professor and Head of Dermatology, Professor of Pathology, Pediatrics, Medicine, and Preventive Medicine and Community Health, Rutgers New Jersey Medical School; Visiting Professor, Rutgers University School of Public Affairs and Administration